I. Field
The following description relates generally to wireless communications, and, amongst other things, to communications in a multiple-carrier, multiple-access communication system.
II. Background
Wireless networking systems have become a prevalent means by which a majority of people worldwide has come to communicate. Wireless communication devices have become smaller and more powerful in order to meet consumer needs and to improve portability and convenience. The increase in processing power in mobile devices such as cellular telephones, personal digital assistants (PDAs) and the like has lead to an increase in demands on wireless network transmission systems.
A multiple-access system can concurrently support communication for multiple mobile devices or terminals. Multiple terminals may simultaneously communicate with a base station of the wireless network transmission system. This simultaneous communication may be achieved by multiplexing the multiple data transmissions such that the data transmissions are orthogonal to one another in time, frequency, code and/or space domain. In general, complete orthogonality is not achieved due to various factors such as channel conditions, receiver imperfections and so on. Nevertheless, substantially orthogonal multiplexing ensures that the data transmission for each mobile device minimally interferes with the data transmissions for the other mobile devices.
In code division multiplexing based techniques, signals are encoded with an orthogonal or semi-orthogonal code type. Code division systems employ codes that facilitate uniquely identifying individual communication channels. Encoded signals are typically interpreted as noise by receivers that do not employ the same code to decode the signal. The number of codes that can be assigned simultaneously is typically limited by the length of the code.
In time division based techniques, a band is split time-wise into sequential time slices or time slots. Each user device assigned to a channel is provided with a time slice for transmitting and receiving information in a round-robin manner. For example, at any given time t, a user device is provided access to the channel for a short burst. Then, access switches to another user device that is provided with a short burst of time for transmitting and receiving information. The cycle of “taking turns” continues, and eventually each user device is provided with multiple transmission and reception bursts.
Frequency division based techniques typically separate the frequency spectrum into distinct channels by splitting the frequency spectrum into uniform chunks of bandwidth. For example, the frequency spectrum or band allocated for wireless cellular telephone communication can be split into 30 channels, each of which can carry a voice conversation or, for digital service, digital data. Each channel can be assigned to only one user device or terminal at a time. One commonly utilized frequency division system is the orthogonal frequency division multiple access (OFDMA) system, which uses orthogonal frequency division multiplexing (OFDM). OFDM effectively partitions the overall system bandwidth into multiple orthogonal frequency channels. An OFDMA system may use time and/or frequency division multiplexing to achieve orthogonality among multiple data transmissions for multiple terminals. For example, different terminals may be allocated different channels, and the data transmission for each terminal may be sent on the channel(s) allocated to this terminal. By using disjoint or non-overlapping channels for different terminals, interference among multiple terminals may be avoided or reduced, and improved performance may be achieved.
The number of channels available for data transmission is limited (to K) by the OFDM structure used for the OFDMA system. The limited number of channels places an upper limit on the number of terminals that may transmit and/or receive simultaneously without interfering one another. In certain instances, it may be desirable to allow more terminals to transmit and/or receive simultaneously, e.g., to better utilize the available system capacity.
A typical wireless communication network (e.g., employing frequency, time, and code division techniques) includes one or more base stations that provide a coverage area and one or more mobile (e.g., wireless) terminals that can transmit and receive data within the coverage area. A typical base station can simultaneously transmit multiple data streams for broadcast, multicast, and/or unicast services, wherein a data stream is a stream of data that can be of independent reception interest to a terminal. A terminal within the coverage area of that base station can be interested in receiving one, more than one or all the data streams carried by the composite stream. Likewise, a terminal can transmit data to the base station or another terminal. Such communication between base station and terminal or between terminals can be degraded due to channel variations and/or interference power variations. For example, the aforementioned variations can affect base station scheduling, power control and/or rate prediction for one or more terminals.
Conventional network data transmission protocols are susceptible to scheduling limitations and transmission capacity limits, resulting in diminished network throughput. Multiple antennas at transmitters and receivers open up space dimensions for data transmission increasing system capacity. With additional space dimensions available, there exists a need in the art for a system and/or methodology of improving throughput and maximizing system capacity in wireless network systems.